One Shoot Two Birds: Stabilization of Mn<sup>5+</sup> in Ba<sub>2</sub>(Si,Ge)O<sub>4</sub> as an Efficient NIR Thermometer and Intense Turquoise Pigment
Wenjing Huang, Chunli Li, Linyun Zeng, Jiahui Zhang, Mikhail A. Kurochkin, Ilya E. Kolesnikov, Zafari Umar, Jilin Zhang, Wei Liu, Ákos Kukovecz, Mekhrdod S. Kurboniyon, Xinguo Zhang
Abstract
Luminescence of transition metal ions in unusual oxidation states is a treasure for developing new phosphors. Pentavalent manganese (Mn 5+ ), which possesses a 3d 2 electron configuration, has been reported less compared to its Mn 2+ and Mn 4+ counterparts due to the difficulty in its stabilization. In this study, Ba 2 (Si 1– x Ge x )O 4:Mn 5+ phosphors were synthesized by a solid-state reaction method. The successful Mn 5+ stabilization in the (Si,Ge)O 4 tetrahedron leads to a bright turquoise body color with a strong NIR-II sharp-peak emission at room temperature. By replacing Si 4+ with Ge 4+, the peak position of the 1 E– 3 A 2 transition remains at 1181 nm, while the corresponding integrated intensity is enhanced by 150% at x = 0.6. First-principles density functional theory (DFT) calculations were performed to explore the geometrically optimized structure and electronic structure variation of the Ba 2 (Si,Ge)O 4:Mn 5+ phosphor. Then, they are discussed in association with the observed luminescence properties. It is found that modification of the host composition could modify the accelerated thermal quenching rate of the 1 E emission. Temperature can be read from Mn 5+1 E vs 3 T 2 luminescence intensity ratios. This work represents a step toward exploring the unusual Mn 5+ as the emitting center for the next-generation NIR-II phosphors and chromophores for new pigments.